(465d) Comparison of MEA and Ammonia for Heat-Integrated Coal-Fired Power Plants with PCC Processes

We have previously studied the energy penalty burdened by integration of pulverized coal-fired power plants with solvent-based post-combustion carbon capture (PCC) processes (Khalilpour and Abbas, 2011). Heat exchanger network (HEN) optimization was, in that study, used to understand the extent of this energy penalty reduction. The base case used was a 300 MWe coal-fired power plant burning pulverized black coal and emitting 256 tonne/h of CO2. Integration of the base case with PCC showed that achieving 90% CO2 capture with purity of 99% using 30 wt% Monoethanolamine MEA solvent admits an energy penalty of 19.4% to the overall plant output. Pinch analysis showed that a reduction of about 18% in overall energy penalty could be achieved.

Finding the ideal solvent is one of the most important cost reduction parameters in the PCC process. Various solvent alternatives are currently being studied to provide improved technical and cost feasibility to the entire project. The kinetics and thus operating conditions of PCC processes running with any given solvent may vary significantly. Therefore, selection of optimal solvents will not be possible unless a holistic systems analysis approach is taken. We propose that this requires consideration of optimal heat integration of the overall power plant-PCC process. Such an optimization is only possible via a model-based approach which is a focus of this current paper.

Monoethanolamine (MEA) has been discussed as having advantages over other solvents in terms of high CO2 reactivity, high absorption capacity and low molecular weight whilst having the drawback of high heat of reaction and thus high regeneration energy requirement (Kohl and Nielsen, 1997). Recent studies, however, challenge the current interest in MEA. Ho et al. (Ho et al., 2009) have compared MEA, KS1 and Potassium Carbonate. Their study shows that the cost of capture using an enhanced potassium carbonate solution is up to 50% less than commercially available amine solvents. Aroonwilas and Veawab (Aroonwilas and Veawab, 2007) have shown that while the reboiler duty for conventional and advanced MEA processes varies in the range of 3.1-4.8 GJ/tonne CO2, the corresponding value for a blend of MEA/MDEA is about 1.2-2.4 GJ/tonne CO2, this being a significant improvement in energy penalty reduction. Another study also shows that promoted amine solutions, e.g. with piperazine, perform better compared to the amines that have not been promoted (Oyenekan and Rochelle, 2007).

Recently ammonia, as a carbon capture solvent, has received increasing attention. In this paper, we compare MEA with Ammonia and study the impact of these two solvents on energy networks of the integrated power plant-PCC process. We then highlight the pros and cons of each followed by their impact on overall energy penalty. 

References

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HO, M. T., ALLINSONA, G. W. & WILEY, D. E. 2009. Factors affecting the cost of capture for Australian lignite coal fired power plants Energy Procedia, 1, 763-770.

KHALILPOUR, R. & ABBAS, A. 2011. HEN optimization for efficient retrofitting of coal-fired power plants with post-combustion carbon capture. International Journal of Greenhouse Gas Control, 5, 189-199.

KOHL, A. L. & NIELSEN, R. 1997. Gas purification, Houston, Tex., Gulf Pub.

OYENEKAN, B. A. & ROCHELLE, G. T. 2007. Alternative stripper configurations for CO2 capture by aqueous amines. Aiche Journal, 53, 3144-3154.